1. Field of the Invention
The present invention relates to an imaging lens, a manufacturing method thereof, and a compound lens. In particular, the present invention relates to an imaging lens having a plurality of lens including a compound lens, a manufacturing method of such an imaging lens, and the compound lens.
2. Description of the Background Art
Recently, an imaging lens for a camera incorporated in a mobile phone, a digital camera or the like, is required to be reduced in size, weight and costs. In such an imaging lens, for example, as shown in FIG. 40, a plurality of lenses 103, 105, 106 are arranged in lens barrel 107. On the light-output side of lens barrel 107, a filter 108 and an imaging element 109 are arranged in order.
Particularly as to the imaging lens for the mobile phone camera, a plastic lens is employed for achieving reduction in weight and costs, as proposed in Japanese Patent Laying-Open No. 2005-345713, for example. There has also been an attempt to employ a compound lens in which a resin lens is bonded to the surface of a plastic lens, so that the total length of the mobile phone camera is reduced and the resolving power is improved.
However, there has been the following problem with a conventional imaging lens. Generally, a plastic lens is formed by molding or the like. In the plastic lens formed by molding or the like, the position of the center of an input-side lens surface (the incident surface center) and that of the center of an output-side lens surface (the output surface center) of the plastic lens not always agree with (positioned at) a prescribed axis in the plastic lens taken out from the mold, such as a center axis for the contour (the contour center axis).
Accordingly, in a state where lenses 103, 105, 106 are assembled in lens barrel 107, lines 121, 122, 123 respectively connecting incident surface centers and output surface centers of lenses 103, 105, 106 may be decentered relative to a barrel center axis 112 of lens barrel 107, resulting in transmission decentration (line 124) taken as a whole lens system. As a result, the light transmitted through lenses 103, 105, 106 does not excellently form an image at imaging element 109, and resolving power is reduced or blurs occur in half of the image.
It is to be noted that, line 121 is a line connecting incident surface center 133a of incident surface 103a and output surface center 133b of output surface 103b of lens 103, line 122 is a line connecting incident surface center 144a of incident surface 105a and output surface center 144b of output surface 105b of lens 105, and line 123 is a line connecting incident surface center 155a of incident surface 106a and output surface center 155b of output surface 106b of lens 106.